A. Field of the Invention
The present invention relates to OSB (oriented strand board) material.
B. Related Art
Oriented strand board, hereinafter termed OSB, is a type of wooden board made from oriented wood flakes. The board consists of a number (generally three) of layers of bonded wood flakes, a maximum of approx. 2 by 15 cm large and a thickness of one half to one-and-a-half mm.
The wood fibres in the outer layers are oriented in a certain direction on average, although not every wood flake is individually precisely oriented, while the flakes in the middle layer are oriented perpendicular to this direction or arbitrarily oriented.
This is a cheap way to obtain a constructional board with very good properties, especially with regard to rigidity, and with optimum use of all parts of a tree.
OSB board material is widely used in constructions, both in applications where the material is not visible, and also on account of its decorative properties.
A disadvantage of such a board material is its combustibility. There are some known ways of making existing board material of wood flakes fire resistant.
For example U.S. Pat. No. 3,874,990 states that moist wood material to be converted into wood flakes for the production of chipboard is mixed with dry alkaline borates, after which the wood material is further moistened and then cut into flakes. A second fire retardant agent, in the form of phosphoric acid-formaldehyde-dicyandiamide resin, is then added to obtain a chipboard with 10 to 16% fire-resistant agent.
This has the disadvantage that it is a complex method and that the second fire-retardant agent is an expensive product.
Furthermore, U.S. Pat. No. 4,039,645 states that moist wood flakes intended for the production of chipboard are treated to this end with a solution of borax decahydrate (Na2B4O7.10H2O) and sulphuric acid, so that a chipboard with approx. 25 parts dry matter, consisting of a mixture of borax and sulphuric acid, per 100 parts dry wood is formed.
High contents of borax are hereby used, such that a relatively expensive board material is obtained. Boron compounds are also suspected of being harmful to health so a high boron content is undesirable.
U.S. Pat. No. 6,713,168 describes how dry wood flakes intended for a board material are mixed with an organophosphorus ester as a fire-retardant agent, in order to obtain a fire-resistant OSB board material with a content of this ester of 5 or 10 percent by weight.
This has the disadvantage that it is an expensive fire-retardant agent.
From U.S. Pat. No. 3,438,847, a chipboard and a method for manufacturing it is known, whereby the chipboard consists of three layers, and is made fire-resistant by introducing boric acid and sodium octaborate in the inner layer and the outer layers, whereby there is a higher concentration of both products in the outer layers than in the inner layer, thereby increasing the fire resistance of a limited quantity of fire-resistant agent.
The fibres for the separate layers are hereby manufactured by completely separate methods.
US 2002/0168476 describes another fire-resistant agent for wood composite: guanylurea phosphate.
This has the disadvantage that it is relatively expensive and that it is relatively easy for NH3 to be released during the manufacture of the wood composite, and thus could lead to a dark discolouring of the wood composite during its manufacture.
These methods, and the materials thereby produced, all have the disadvantage that the quantity and nature of the fire-retardant agents are not optimum to obtain sufficient fire-resistant properties of the OSB board material at the lowest possible cost price, whereby negative influences during production or on the quality of the OSB board material produced are minimised.